This one is about perspective.
The old, fallen gravestone bears no name. Time and weather have erased it (if there ever was one).
For the vast majority of us--in not too many generations--even our names will be forgotten and gone, and any enduring contributions will be quite anonymous--just like the influences of our own great-grandparents on us today.
(As for the title, John or Jane Doe are, of course, the names used in many English-speaking countries as placeholders for unidentified, anonymous. or hypothetical persons.)
From On Cemetery Grounds